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The following page has been changed by MichaelJouravlev: http://wiki.apache.org/struts/StrutsComponents New page: #format wiki #language en Struts 1.3.x (TBD) allows building portlet-like web components using JSP as view technology. The components work properly with or without Javascript enabled. Struts Components have the following features: * Allows composing a page out of one or more independent components. * Renders a view that is always synchronized with application state. * Solves major issues related to stale pages and double submits. * Delivers input directly to a component, no central controller is needed * Ensures that every component renders itself independently. * Updates page incrementally without full page refresh if browser has Javascript turned on and XMLHTTPRequest is available. * Seamlessly integrates with Struts, enhancing a well-known action framework with component technology. == Use Case: Home Page With Login Component == Consider the following use case: a website has a home page that should have different content for regular visitors one one hand, and for logged in users for another hand. The page contains login/logout form, a user must be presented with login form if he is not logged in yet. Those users who logged in must be able to see information about themselves and must be able to log out. While implementing this use case the login/logout widget must reload the whole page if login attempt fails. Also, login/logout widget must have explicit knowledge about the target location, in our case it has to know the address of the home page. Therefore, it is nearly impossible to develop an independent login/logout widget that can be inserted into different pages and just work. Well, it is possible now. == Component Configuration == The Struts Web Component is represented with one Action class and with one (or more) JSP pages. Let us define the Login Component in struts-config.xml file: {{{ <struts-config> <form-beans> <!-- Login form --> <form-bean name = "loginform" type="samples.login.LoginForm"/> </form-beans> <action-mappings> <!-- Composite page containing login component --> <action path="/login-struts" forward="/login-struts/index.jsp"/> <!-- Login component --> <action component = "Login" view = "/login-struts/loginComponent.jsp" path = "/loginintegrated" type = "samples.login.LoginAction" form = "loginform" scope = "session" validate = "false"> <event name="loginEvent" handler="login"/> <event name="logoutEvent" handler="logout"/> </action> </action-mappings> </struts-config> }}} Notice new action mapping attributes and properties: * "component" attribute identifies an action as a component manager, such actions are processed differently by Action class. This name is also used in generated HTML for in-place update in Ajax mode. * "view" attribute identifies a default view for a component. Must be a JSP page. Often consists from several subviews, in our case the Login Component has two subviews "Not Logged In" and "Logged In", they will be defined in JSP file. * "form" is just another name for "name" property * "event" property allows to define request parameters as events, and corresponding method handlers. That is right, dispatching functions are now supported in the core Struts, by Action class. == Component Action == The action class is deceptively simple. It handles only two events, the corresponding handlers are called automatically by Action class. The location of component's view is defined in the action mapping, so render method is not needed. On the other hand, most non-trivial components need to process data before rendering themselves or to exchange data with other components. For these cases you can use render" method. Its default implementation does nothing. {{{ public class LoginAction extends Action { public ActionForward login (ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { HttpSession session = request.getSession(); LoginForm inputForm = (LoginForm) form; // Log out current user first request.getSession().removeAttribute("USER"); // Validation is turned off in struts-config.xml, // so explicitly validate user input; ActionMessages errors = inputForm.validate(mapping, request); if (errors != null) { saveErrors(session, errors); } else { // Use this session attribute to hold user's name session.setAttribute("USER", inputForm.getUsername()); } // Always return null. return null; } public ActionForward logout (ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { LoginForm inputForm = (LoginForm) form; // Clean name and password in the input/output form bean inputForm.setUsername(null); inputForm.setPassword(null); // Remove dialog name from session, effectively logging out request.getSession().removeAttribute("USER"); // Always return null. return null; } } }}} == Component Form Bean == Nothing exciting here, just a session-scoped form to hold user name and to validate credentials: {{{ public class LoginForm extends ActionForm { private String username; public String getUsername() {return username;} public void setUsername(String username) {this.username = username;} private String password; public String getPassword() {return password;} public void setPassword(String password) {this.password = password;} // Generate the error messages in the same manner as usual, // but do not forget to turn "validate" property of the action mapping off. public ActionErrors validate(ActionMapping mapping, HttpServletRequest request) { if (!"guest".equalsIgnoreCase(username) || !"pass".equalsIgnoreCase(password)) { ActionErrors errors = new ActionErrors(); errors.add("ERROR", new ActionMessage("login.badpassword")); return errors; } else { return null; } } } }}} == Login/Logout JSP page == The Login/Logout component has two subviews, both defined in one JSP page. Notice that content type is set to "text/xml", this is important for Ajax mode. {{{ <%@ page contentType="text/xml;charset=UTF-8" language="java" %> <%@ page import="java.util.ArrayList, org.apache.struts.Globals"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"; %> <%@ taglib uri="http://struts.apache.org/tags-bean"; prefix="bean" %> <%@ taglib uri="http://struts.apache.org/tags-html"; prefix="html" %> <%@ taglib uri="http://struts.apache.org/tags-logic"; prefix="logic" %> <%@ taglib uri="http://struts.apache.org/tags-comp"; prefix="comp" %> <comp:component> <%-- "Not Logged In" subview --%> <c:if test='${empty USER}'> <h3>Please Log In</h3> <!-- Displaying Struts errors --> <logic:messagesPresent> <html:messages id="error"> <li><bean:write name="error"/></li> </html:messages> </logic:messagesPresent><br/> <%-- "strutsCommand" CSS class is a hook for Ajax-mode handler, it is set in runtime using Behaviour library. --%> <html:form method="get" styleClass="strutsCommand" action="/loginintegrated.do"> <label for="username">Username:</label> <input type="text" name="username" value="${loginform.username}" class="datavalue"/><br/> <label for="password">Password:</label> <input type="text" name="password" value="" class="datavalue"/><br/> <input type="submit" name="loginEvent" value="Log In" class="strutsCommand"/> </html:form> <p><em>Username is "guest", password is "pass".</em></p> </c:if> <%-- "Logged In" subview --%> <c:if test='${not empty USER}'> <h3>User Information</h3> <html:form method="post" styleClass="strutsCommand" action="/loginintegrated.do"> <label>Current user:</label> <div class="datavalue">${USER}</div><br/> <input type="submit" name="logoutEvent" value="Log Out" class="strutsCommand"/><br/> </html:form> </c:if> </comp:component> }}} == Composite Page == Now we need to include the Login Component into a larger page (composite page). This is done with JSTL c:import tag. Do not use jsp:include, it may not work on some containers: {{{ <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"; %> <%@ taglib uri="http://struts.apache.org/tags-html"; prefix="html" %> <%@ taglib uri="http://struts.apache.org/tags-comp"; prefix="comp" %> <html> <body> <p>This paragraph is defined directly in the parent page and should precede the content of login control.</p> <%-- The login component, notice that DIV has the same ID as the component's name --%> <div id="Login"> <c:import url="/loginintegrated.do" /> </div> <p>This paragraph is defined directly in the parent page and should follow the content of login control.</p> </body> </html> }}} == Done! == This is pretty much it. Now run the application and navigate to composite page. The included component will evaluate user's state and will display a login form. Try to log in. The submitted credentials are sent directly to a component, if they are not correct, the composite page is redisplayed. How? Behind the scenes the improved Action class as well as JSP tags work together to distinguish the address of a composite page during first render. This address is saved automatically. Then after component finishes, it reloads the composite page using saved address. Now you can develop independent Struts components! Next installment: making components that update themselves in place without full page reload (Ajax mode).
